The present invention relates to a gas shielding apparatus and a gas shielding method. More particularly, it relates to improvement of gas shielding in bonding portion or heating area in a diffusion bonding or high frequency hardening.
Hitherto, in order to prevent oxidation of a bonding surface in diffusion bonding, as shown in FIG. 8, diffusion bonding is conducted by covering the bonding and heating area with a gas jacket 10'. Besides, since there is a gap between this gas jacket 10' and members to be bonded P, P penetrating through the gas jacket 10', in order to prevent invasion of air into the gas jacket 10', inert gas (hereinafter called shielding gas) is supplied into the gas jacket 10' from a nozzle 11', and diffusion bonding is carried out while shielding the heating zone. That is, the shielding gas leaks out from the gap between the member to be bonded (member to be heated) P, P of the gas jacket 10', and diffusion bonding is performed while preventing invasion of air into the gas jacket 10' from outside. In FIG. 8, reference numeral 12' shows an induction heating coil.
However, when diffusion bonding is done while leaking out the shielding gas as shown in FIG. 8, a gas flow is formed in the gas jacket 10', and the outside of the bonded joint J is cooled by this gas flow. As a result, the bonded joint J is not sufficiently heated, which may lead to decline of quality of the bonded interface or decline of bonding strength.
Such problems similarly occur in high frequency hardening in which gas shielding is effected by using a gas jacket.
The invention is devised in the light of the problems of the prior art, and it is hence an object thereof to present a gas shielding apparatus and a gas shielding method not causing decline of quality of the bonding portion or heating area and decline of strength.